There's a lot going on in a racing stable to get a person sneezing — shaking out straw bedding, raking loose dirt aisles, sweeping dusty feed rooms. Research and commentary presented at the recent Welfare and Safety of the Racehorse Summit suggested many traditional components of horsekeeping at the track could be wreaking havoc on horses' airways, too.
The summit, hosted by the Grayson-Jockey Club Research Foundation, featured talks from Dr. Susan Holcombe of Michigan State University's College of Veterinary Medicine and veteran owner/breeder Bill Casner.
Longtime horsemen know lung health is crucial to a horse's athletic performance, but Holcombe presented some interesting numbers about the prevalence of airway disease and impact of reduced oxygen flow. Horses have more mitochondria in their muscle cells than almost any other mammal, and those structures rely on oxygen to help the muscle function. This is why horses' athletic performance is limited not by their heart's ability to function (as is true for humans) but by their lungs.
A horse's lung capacity increases almost 30-fold from rest to racing, moving five liters of air per breath. According to Holcombe, this is why a horse with an inflamed airway can appear to be breathing well in the stall but will experience reduced performance during exercise. Current research indicates that inflammatory airway disease, one cause of poor respiratory health, may impact as much as 33 percent of the racehorse population. Horses with IAD won't have fevers, appear depressed, or lose weight. Some may not even cough. Allergens, particulates (including dust), and endotoxins are known to cause inflammation and production of mucus characteristic of IAD.
“When horses (and people) breathe these things in, it will induce an inflammatory change in the lung,” said Holcombe. “Not only does it cause inflammation within the lung, that inflammation will also diminish the lung's immune responsiveness. Horses (like people) are then less able to fight viruses and bacterial infections.”
Where are these floating particles and toxins coming from? Holcombe said they're in the air inside the barn, where racehorses spend most of their day. She showed diagrams of three different barns at an unidentified racetrack where particulate concentration was measured in the air at several points throughout the day. Results were color-coded, and in some cases, white stalls (those with very little dust) were across from or even next to amber or red-colored stalls. Amber or red stalls were those whose dust concentration exceeded Occupational Safety and Health Administration parameters for humans. More mucus was found in the tracheas of horses in those amber and red stalls than those in the white stalls.
“We know that when horses inhale dust, we will see changes in their lung and their lung function within 20 minutes,” she said. “Not only is that a health issue and maybe a humane concern for horses, it's also very important for performance.”
Stall cleaning, feeding, raking, and feeding from haynets were all associated with higher dust readings in Holcombe's study. Haynets are problematic because horses pull mouthfuls of hay into the stall, flinging dust around their faces as they do so.
Bill Casner said Holcombe's results were of little surprise to him. He said he had long watched horses move in and out of stalls, wondering what the years-old layers of dust (and bacteria) could be doing to them. Casner believes the design of most racetrack barns — low ceilings with hay and straw above — lends itself to mold growth, and lots of ammonia, dust, and bits of straw trapped inside. Muck pits outside the barn also stir up dirt when they're filled and emptied each morning.
Casner developed a number of preventative techniques to reduce the risk of airway inflammation or infection. He designed the training barn at WinStar Farm, which has a high ceiling with skylights, open-front stalls, giant overhead fans, and windows to keep air flowing. He also limits bedding to shavings or wood pellets rather than straw, which tends to be dusty, especially if it is poor quality. Hay is given in corner feeders on the ground, minimizing the stirring of particulates, and hay is steamed whenever possible.
Besides dust, Casner said he has struggled with bacteria lurking in stalls.
“The biggest challenge in trying to achieve a clean respiratory environment is the challenge of years of accumulated pathogens and contaminants in that stall,” said Casner. “When I was training in the 1970s, I trained at Oaklawn Park and was assigned the same stalls every year. I had a horse each year get a terrible case of skin disease out of the same stall. The symptoms were always exactly the same. After the third horse got it, I put two and two together and started power-washing and disinfecting my stalls before we moved in.”
It isn't typical for racetrackers to power-wash or even scrub down stalls before moving their horses in at the start of a meet and certainly not between horses once racing has started, Casner said. He has started a routine of fogging all stalls every two weeks to kill bacteria, viruses, and biofilms.
This routine could prove helpful not only to racetrackers, but also to farm managers. Casner suspects the mild respiratory infection often seen in weanlings (often called “baby crud”) isn't a normal part of growing up for young horses but a sign of environmental contamination. Traditional wisdom suggests the “baby crud” is necessary for horses to build their immune systems; in reality, horses develop immunity only to the particular version of virus or bacteria that made them sick. One round of “crud” does nothing for their immune system at large, according to researchers Casner has consulted. That was enough for him to change the routine at the barn where he keeps his breeding stock.
“That was always my first question when I'd hit the barn in the morning — 'Who's got a temp?'” said Casner. “Three years ago we started fogging the stalls twice a week with an antimicrobial, before the fourth group that I brought in. Amazingly enough, we have not had one cough, not one snot, and not one temperature in the last three years [since.]”
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